1. Field of the Invention
The present invention relates to an acceleration sensor in which an actuating member is moved from a non-actuating position to an actuating position, at which the actuating member actuates an occupant protecting device, by inertial movement of an inertial mass which is caused by application of acceleration to the inertial mass when a vehicle suddenly decelerates.
2. Description of the Related Art
An air bag device is known as a device for protecting an occupant of a vehicle.
In an air bag device, when a vehicle suddenly decelerates, an air bag inflates so that an occupant is protected. An acceleration sensor is used to actuate the air bag device when the vehicle suddenly decelerates.
As illustrated in FIG. 5, conventionally, a ball 80 is used as an inertial mass. The ball 80 is provided so as to be able to move inertially when a vehicle suddenly decelerates. When the ball 80 moves inertially, an end portion of the lever 82 ( i.e., the left end portion as illustrated in FIG. 5 ) is pushed toward the front of the vehicle (i.e., in the direction of the FR arrow) by the ball 80. (Hereinafter, the front of the vehicle will be denoted by the FR arrow). The lever 82 rotates around a rotation shaft 84, which is formed so as to project at both end surfaces in the longitudinal direction (i.e., the direction orthogonal to the surface of the paper in FIG. 5) of a trigger member 100 which is provided at a longitudinally intermediate portion of the lever 82.
An ignition pin 86 serving as an actuating member is provided at the longitudinally intermediate portion of the lever 82. The ignition pin 86 is movable, in a direction parallel to the direction of inertial movement of the ball 80, from a non-actuating position, at which an unillustrated detonator is not actuated, to an actuating position, at which the ignition pin 86 ignites the detonator. A bias pin 102, which is urged toward the front of the vehicle by a bias spring 92, abuts the other end portion of the lever 82 (i.e., the right end portion as illustrated in FIG. 5). The bias spring 92 exhibits resistance against inertial movement of the ball 80 caused by deceleration, vibration and the like which are generated under normal running conditions of the vehicle. Therefore, inertial movement of the ball 80 is prevented. Accordingly, the engaging of a trigger portion 90 and an engaging collar 88 of the ignition pin 86 is not canceled, and the ignition pin 86 is not inadvertently moved.
Normally, the engaging collar 88 provided at the longitudinally intermediate portion of the ignition pin 86 is engaged with the trigger portion 90, and the ignition pin 86 is maintained at the non-actuating position, at which the detonator is not actuated. However, when the vehicle suddenly decelerates, the lever 82 is rotated by the inertial movement of the ball 80 towards the front of the vehicle against the urging force of the bias spring 92, and the engagement of the trigger portion 90 and the engaging collar 88 is canceled. Due to this cancellation, the ignition pin 86 is moved by the urging force of an ignition spring 94 toward the actuating position at which the detonator is actuated. The ignition pin 86 abuts the detonator, and the detonator ignites. Due to the ignition of the detonator, a gas-generating material combusts, and gas is generated. The generated gas is supplied to the interior of the air bag, and the air bag inflates.
However, in the above-described conventional acceleration sensor, the bias spring 92 is provided separately from the ignition spring 94 which applies the force for ignition by urging the ignition pin 86 to move to the actuating position. This results in an increased number of structural parts and in troublesome assembly.
Further, in this conventional acceleration sensor, the trigger member 100, at which the trigger portion 90 is formed, is manufactured from a cylindrical member 150 by a number of processes, as can be seen from FIG. 6. Namely, both axial direction end portions of the cylindrical member 150 are cut (i.e., the rotation shaft 84 is formed), a longitudinally intermediate portion of the cylindrical member 150 is cut in order to form the trigger portion 90, a lever insertion hole 102, in which the lever 82 is inserted, is formed, and the like. Further, there is work involved in inserting the lever 82 in the lever insertion hole 102 and work involved in other processes as well. The processing of the trigger member 100 and the number of stages involved in assembly lead to an increase in the manufacturing cost of the conventional acceleration sensor.